The selection index and single- and multi-trait animal model evaluation of Polish Black-and-White cows
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The selection index and single- and multi-trait animal models were used for genetic evaluation of 100,983 cows. Genetic and environmenta? al (co)variances of five milk production traits were estimated using MTDFREML. The highest heritabilities were found for fat and protein contents in all three lactations (0.29-0.33), and the lowest for protein yield in the third lactation (0.08). Phenotypic and genetic correlations between yield traits in adjacent lactations were higher than between the first and third lactations. Correlations between breeding values for fat content were higher than for yield traits. The magnitude of correlations between the index and animal model evaluations depended on the number of lactation records included in both procedures. Usually the relationships between breeding values based on the same lactations were close to unity. The correlations between single-trait and multi-trait evaluations decreased with increasing numbers of lactations in the model. This was the result of using variances and covariances of later lactations in the multi-trait model.
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W. Jagusiak, Department of Genetics and Animal Breeding, Agricultural University, Al. Mickiewicza 24/28, 30-059 Krakow, Poland, email: email@example.com.